A network administrator is configuring a new IPsec VPN tunnel on FortiGate. The remote peer IP address is dynamic, in addition, the remote peer does not support a dynamic DNS update service. What…

Configuring a 'Static IP Address' for the remote gateway would prevent the tunnel from establishing because the remote peer's IP address is dynamic and will not match the configured static IP.

When the remote IPsec peer has a dynamic IP address and cannot use dynamic DNS, configuring the FortiGate's remote gateway as 'Dialup User' allows it to act as a VPN server. In this mode, the FortiGate listens for incoming VPN connections from clients whose IP address is unknown or changes, rather than initiating a connection to a specific, fixed IP.

The 'Dynamic DNS' option is unsuitable because the question explicitly states that the remote peer does not support a dynamic DNS update service, meaning its dynamic IP cannot be registered and resolved by a hostname.

A 'Pre-shared Key' is a method of authentication for the VPN tunnel, not a type of remote gateway configuration that addresses the dynamic IP challenge.